1,3-Butadiene (hereinafter butadiene) is an important monomer for the production of synthetic rubbers including styrene-butadiene-rubber (SBR), polybutadiene (PB), styrene-butadiene latex (SBL), acrylonitrile-butadiene-styrene resins (ABS), nitrile rubber, and adiponitrile, which is used in the manufacture of Nylon-66 (White, Chemico-Biological Interactions, 2007, 166, 10-14). Butadiene is typically produced as a co-product from the steam cracking process, distilled to a crude butadiene stream, and purified via extractive distillation (White, Chemico-Biological Interactions, 2007, 166, 10-14). Industrially, 95% of global butadiene production is undertaken via the steam cracking process using petrochemical-based feedstocks such as naphtha. Butadiene has also been prepared, among other methods, by dehydrogenation of n-butane and n-butene (Houdry process) and oxidative dehydrogenation of n-butene (Oxo-D or O—X-D process) (White, Chemico-Biological Interactions, 2007, 166, 10-14). These methods are associated with high cost of production and low process yield (White, Chemico-Biological Interactions, 2007, 166, 10-14).
Isoprene is an important monomer for the production of specialty elastomers including motor mounts/fittings, surgical gloves, rubber bands, golf balls and shoes. Styrene-isoprene-styrene block copolymers form a key component of hot-melt pressure-sensitive adhesive formulations and cis-poly-isoprene is utilised in the manufacture of tires (Whited et al., Industrial Biotechnology, 2010, 6(3), 152-163). Manufacturers of rubber goods depend on either imported natural rubber from the Brazilian rubber tree or petroleum-based synthetic rubber polymers (Whited et al., 2010, supra).
Given a reliance on petrochemical feedstocks and energy intensive catalytic steps, biotechnology offers an alternative approach to butadiene and isoprene synthesis via biocatalysis. Biocatalysis is the use of biological catalysts, such as enzymes, to perform biochemical transformations of organic compounds. Accordingly, there is a need for sustainable methods for producing butadiene and isoprene, wherein the methods are biocatalyst-based (Jang et al, Biotechnology & Bioengineering, 2012, 109(10), 2437-2459). Both bioderived feedstocks and petrochemical feedstocks are viable starting materials for the biocatalysis processes.